1. Field of the Invention
The present invention relates to a method and apparatus for measuring flow velocity of a fluid and a method and apparatus for measuring flow rate of a fluid by using a signal sound, mainly, ultrasound.
2. Description of the Related Art
In recent years, there is a current meter for measuring flow velocity of a fluid by using ultrasound.
The ultrasound flow velocity meter is constructed by disposing two oscillators with a spacing in the longitudinal direction in a tube member through which a fluid flows. Ultrasound is transmitted from one of the oscillators and received by the other oscillator, and ultrasound is transmitted from the other oscillator and received by the one of the oscillators. From the difference between the propagation time of the ultrasounds, the flow velocity of the fluid in the tube member is obtained. The flow rate is derived by multiplying the flow velocity with the internal diameter of the tube member.
Although the conventional ultrasound flow velocity meter uses a measuring method such as a time difference method or a phase difference method, if the spacing between the two oscillators is short, the time difference or phase difference is minute. Naturally, an error becomes big.
The propagation speed of ultrasound changes according to the temperature, pressure, and kind of a fluid. The changes may be ignored as errors, but they become a problem in the case of measuring flow velocity with high precision.
Similarly, they become a problem in the case of measuring the flow rate with high precision.
The present invention has been achieved in consideration of the circumstances as described above and its object is to provide a method and apparatus for measuring flow velocity and a method and apparatus for measuring flow rate, capable of measuring flow velocity and flow rate with high precision.
According to a first aspect of the present invention, there is provided a flow velocity measuring method for measuring flow velocity of a fluid that flows, comprising: a step of allowing a signal sound to propagate to the upstream or downstream side in a fluid and detecting a phase difference between the signal sound and an original signal; a step of eliminating a phase difference detected in the step and synchronizing the phases; a step of detecting time or oscillation frequency required to complete the phase synchronization in the step; and a step of calculating flow velocity of the fluid with reference to the flow velocity preset in correspondence with the time or oscillation frequency on the basis of the time or oscillation frequency required to complete the phase synchronization in the step.
According to the first aspect, the higher the flow velocity of a fluid is, the larger the phase difference is. When the phase difference becomes large, in proportion to the phase difference, the time required to synchronize phases becomes long and the change in oscillation frequency becomes large. When the relation between the flow velocity of a fluid and time or oscillation frequency required to synchronize phases is preset, by referring to the preset flow velocity on the basis of the detected time or oscillation frequency, the flow velocity of a fluid can be calculated. As a result, the phase difference as a minute numerical value can be accurately replaced with time or oscillation frequency required to synchronize phases as a relatively large numerical value, and the flow velocity can be measured with high precision.
According to a second aspect of the present invention, there is provided the flow velocity measuring method in the first aspect, wherein flow velocities are preset in correspondence with not only the time or oscillation frequency but also changes in temperature, pressure, and kind of a fluid.
According to the second aspect, correction can be made in correspondence with a change in temperature, pressure, and kind of a fluid. Since the phase difference changes according to the temperature, pressure, and kind of a fluid, the flow velocities are preset in association with changes in temperature and the like. Thus, even when the temperature, pressure, or kind of a fluid changes, the flow velocity can be obtained with high precision.
According to a third aspect of the present invention, there is provided the flow velocity measuring method in the first or second aspect, wherein phase difference detection performed by making signal sound propagate to the upstream side in the fluid and phase difference detection performed by making signal sound propagate to the downstream side in the fluid are alternately switched, and a calibration signal is output at the time of switching to prevent a fluctuation at the time of switching.
According to the third aspect, signals are propagated to both the upstream and downstream sides and a phase difference between the signals is detected. Flow velocities are obtained with respect to two phases deviated to the opposite directions and averaged, thereby improving the reliability of a measured value. At the time of switching the propagation direction of a signal sound, a calibration signal is output. The propagation of a signal sound may be fluctuated at the time of switching the direction of propagation of the signal sound between the upstream side and the downstream side. There is a case such that the propagating signal sound becomes extremely large or small and a measurement value largely fluctuates. To solve the problem, a calibration signal is output to prevent a fluctuation at the time of switching, that is, a large fluctuation in the measurement value. With the configuration, the flow velocity can be measured with high precision.
According to a fourth aspect of the present invention, there is provided the low velocity measuring method in the third aspect, wherein the frequency of the calibration signal output at the time of switching is modulated in correspondence with a change in temperature, pressure, and kind of the fluid.
According to the fourth aspect, the calibration signal whose frequency is modulated in correspondence with a change in temperature or the like of a fluid is output at the time of switching. Consequently, even if a change in the temperature or the like of a fluid is large, the flow velocity can be measured with high precision.
According to a fifth aspect of the present invention, there is provided a flow velocity measuring apparatus for measuring flow velocity of a fluid which flows, comprising: a plurality of signal sound transmitting/receiving units disposed in a fluid that flows, for transmitting/receiving a signal sound; a phase difference detecting unit for detecting a phase difference between a signal sound properly transmitted and received by the plurality of signal sound transmitting/receiving units to thereby allow the signal sound to propagate to the upstream or downstream side in the fluid and the original signal; a phase synchronizing unit for eliminating a phase difference detected by the phase difference detecting unit to obtain synchronization; a detecting unit for detecting time or oscillation frequency required to complete the phase synchronization in the phase synchronizing unit; and a flow velocity calculating unit for calculating flow velocity of the fluid by referring to, on the basis of the time or oscillation frequency detected by the detecting unit, flow velocity which is preset in correspondence with the time or oscillation frequency.
According to the fifth aspect, when two signal sound transmitting/receiving units are disposed in a fluid, a signal sound is transmitted from one of the signal sound transmitting/receiving units and received by the other unit. Transmission and reception are alternately switched between the two signal sound transmitting/receiving units, and a signal sound is allowed to propagate to the upstream and downstream sides in the fluid. Further, when three signal sound transmitting/receiving units are disposed in a fluid, the signal sound transmitting/receiving unit in the center is used as a transmission side, and the signal sound transmitting/receiving units on both sides are used as a reception side. A signal sound from the signal sound transmitting/receiving unit in the center is simultaneously propagated to the upstream and downstream sides. When four signal sound transmitting/receiving units are disposed in a fluid, they are divided into two groups. A signal sound is allowed to propagate to the upstream side in one of the groups, and a signal sound is allowed to propagate to the downstream side in the other group. When five or more signal sound transmitting/receiving units are provided, the example of two units and the example of three units are combined. By the signal sound transmitting/receiving units, the signal sound is allowed to propagate to the upstream or downstream side in the fluid, the phase difference between the signal sound and the original signal is detected by the phase difference detecting unit, and the phase difference is eliminated to synchronize phases by the phase synchronizing unit. The time or oscillation frequency required to complete the phase synchronization is detected by the detecting unit. On the basis of the time or oscillation frequency, by referring to a preset flow velocity, the flow velocity of the fluid is calculated in the flow velocity calculating unit. As a result, the flow velocity can be measured with high precision.
According to a sixth aspect of the present invention, there is provided the flow velocity measuring apparatus in the fifth aspect, wherein the signal sound transmitting/receiving units are disposed in a tube member through which a fluid is passed, and measure flow velocity of the fluid in the tube member.
According to the sixth aspect, the signal sound transmitting/receiving unit allows the signal sound to propagate to the upstream or downstream side in a tube member, and the flow velocity of the fluid in the tube member can be measured from the outside.
According to a seventh aspect of the present invention, there is provided the flow velocity measuring apparatus in the fifth or sixth aspect, wherein flow velocities corresponding to changes in temperature, pressure, and kind of the fluid are preset in the flow velocity calculating unit.
According to the seventh aspect, in correspondence with a change in temperature, pressure, or kind of a fluid, the detection value can be corrected. Although the speed of a signal sound propagating through a fluid changes according to the temperature or the like of the fluid, by presetting flow velocities corresponding to changes in temperature and the like of the fluid in the flow velocity calculating unit, an error caused by a change in the temperature and the like of the fluid can be corrected. That is, although the phase difference slightly changes according to the temperature or the like of a fluid, by presetting the flow velocity corresponding to the temperature or the like in association with a flow velocity as a reference, the change in the phase difference is absorbed. As a result, even when the temperature or the like in the fluid changes, the flow velocity can be measured with high precision.
According to an eighth aspect of the present invention, there is provided the flow velocity measuring apparatus in any one of the fifth to seventh aspects, wherein three signal sound transmitting/receiving units are provided at equal intervals in the direction of flow of a fluid, the signal sound transmitting/receiving unit in the center transmits a signal sound, the signal sound transmitting/receiving units on both sides receive the signal sound, the signal sound is propagated simultaneously to the upstream and downstream sides only by the same distance in the fluid, and the phase difference is detected.
According to the eighth aspect, an average of the phase difference detected by allowing a signal sound to propagate to the upstream side and the phase difference detected by allowing a signal sound to propagate to the downstream side is calculated. Thus, the flow velocity can be measured with higher precision.
According to a ninth aspect of the present invention, there is provided the flow velocity measuring apparatus in any one of the fifth to eighth aspects further comprising: a switching unit for alternately switching phase difference detection performed by making signal sound propagate to the upstream side in the fluid and phase difference detection performed by making signal sound propagate to the downstream side in the fluid; and a calibration signal oscillating unit for oscillating a calibration signal at the time of switching performed by the switching unit to thereby prevent a fluctuation at the time of switching.
According to the ninth aspect, the signal sound propagating direction is switched by the switching unit, and phase differences in both directions are detected and averaged. At the time of switching performed by the switching unit, there is a case such that signals are lost, canceled out, or enhanced and a large fluctuation occurs. Consequently, at the time of switching, a calibration signal is oscillated by the calibration signal oscillating unit, and a process is performed with an average value only at the time of switching. Consequently, a large fluctuation in the phase difference can be prevented, and the flow velocity can be measured with higher precision.
According to a tenth aspect of the present invention, there is provided the flow velocity measuring apparatus in the ninth aspect, wherein the frequency of the calibration signal output from the calibration signal oscillating unit at the time of switching is modulated in correspondence with a change in temperature, pressure, and kind of the fluid.
According to the tenth aspect, the calibration signal whose frequency is modulated in correspondence with a change in temperature or the like of a fluid is output by the oscillating unit at the time of switching. Consequently, even when a change in temperature or the like of a fluid is large, the flow velocity can be measured with high precision.
According to an eleventh aspect of the present invention, there is provided a flow rate measuring method comprising: a flow velocity measuring step using the flow velocity measuring method according to any one of first to fourth aspects; and a flow rate measuring step of measuring a flow rate by multiplying the flow velocity obtained in the flow velocity measuring step with an internal diameter of a tube member through which a fluid flows.
According to the eleventh aspect, on the basis of the flow velocity measured with high precision, the flow rate can be measured with high precision.
According to a twelfth aspect of the present invention, there is provided a flow rate measuring apparatus comprising: a flow velocity measuring unit using the flow velocity measuring apparatus according to any one of the fifth to tenth aspects; and a flow rate measuring unit for measuring a flow rate by multiplying flow velocity obtained by the flow velocity measuring unit with the internal diameter of a tube member through which a fluid flows.
According to the twelfth aspect, the flow rate can be measured with high precision on the basis of the flow velocity measured with high precision.